This invention relates to an apparatus for gripping a down hole tubular for support and rotation using two-part gripping elements which include a lower gripping part that is shaped to engage a tapered shoulder of a down hole tubular to support the down hole tubular, and an upper gripping part that is shaped to engage a tool joint of the down hole tubular to rotate the down hole tubular.
Drilling tubulars such as drill pipe are exposed to constant wear and abuse. Wear occurs chiefly at the tool joints, because making up operations, breaking out operations, spinning in operations and spinning out operations gradually wear the tool joint threads and shoulders. Such wear plus the inevitable dents, scratches and the like are typically corrected by re-machining the surfaces. Additionally, the outer cylindrical surfaces of tool joints are continuously abraded during drilling operations as they rub against the inside diameter of the casing and the uncased hole, i.e. directly on the formation being drilled. This type of wear cannot be corrected economically, and for this reason it is important for make-up/break-out tooling designed to clamp on the outer cylindrical surfaces of tool joints to compensate for such wear as it occurs.
Furthermore, drilling tubulars often become slightly bent, chiefly as a result of abuse during moves from one drill site to another, but also as a result of routine drilling operations. Tooling designed to clamp on the outer cylindrical surfaces of tool joints for spinning operations, as well as for make-up/break-out operations, must itself center the upper tool joint of the uppermost length of drill pipe, or alternatively be equipped with a separate centering means.
U.S. Pat. No. 5,036,927, assigned to the assignee of this invention, discloses an apparatus for gripping a down hole tubular such as casing for rotation. The disclosed apparatus includes a set of one-piece gripping elements or dogs 50, 150 which are moved vertically along inclined guides so as to grip either the inside or the outside of the casing.
Although these one-piece gripping elements perform well when making up casing, they are not well suited to compensate for the differing rates of wear on the tool joint outer cylindrical surface, the 18.degree. tapered shoulder at the base of the tool joint, and the outer cylindrical surface of the body of the drilling tubular. This is because the outer cylindrical surface of the tool joint typically wears much faster than the latter two surfaces (except in the case of drilling with air, which may cause the 18.degree. tapered shoulder at the base of the tool joint to wear out as fast or faster than the tool joint outer cylindrical surface).
Brown U.S. Pat. No. 3,915,244 discloses a break-out elevator which as shown in FIG. 2 includes two-part gripping elements. The lower parts 68 are shaped to engage the 18.degree. tapered shoulder adjacent the tool joint, and the upper gripping elements 73 are shaped to engage the outer cylindrical surface of the tool joint for rotation. Brown discloses a system using hydraulic cylinders and pistons as shown in FIG. 7 to raise and lower the upper and lower gripping elements 73,68 together. In the disclosed system the upper and lower gripping elements are guided for relative movement by guides 72 that are oriented transversely to the drilling axis. Thus, vertical movement of the gripping elements is not effective to move the upper gripping element inwardly with respect to the lower gripping element. Instead, this function is performed by rollers 91 which cooperate with cam surfaces 73 as shown in FIG. 7.